Coronavirus Testing Explained: Serological Testing and Immunoglobulin Therapy

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Published on Apr 11th, 2020

Determining who can come into contact with the novel coronavirus without getting sick is becoming a new focus in the battle against COVID-19. To stop the spread of the virus, scientists need to think outside the box rather than focus on testing alone.

In an earlier article, we discussed the two types of testing for SARS-CoV-2: PCR testing and Antibody testing. In this article, we will focus on serological (antibody) testing and immunoglobulin therapy, and we will also discuss why we should look forward to more benefits from testing than just identifying active cases.

Serological Testing

Testing for IgG and IgM Antibodies

Antibodies, also known as immunoglobulins, are used by the immune system to identify and destroy foreign objects such as bacteria and viruses. The body produces five isotypes of antibodies. Two of the five antibodies, IgM and IgG, are important in serological testing.

IgM antibodies IgG antibodies

IgM antibodies are the largest antibodies in the body. When there is an infection, the body responds quickly by producing IgM antibodies first.

IgM antibodies make up about 5% to 10% of all the antibodies in the body and are found in the blood and lymph fluid. Scientists can use IgM panels to detect an “acute infection” of the SARS-CoV-2 virus because the body makes these antibodies first.

IgG antibodies are the smallest and most common antibodies and they are found in all body fluids. They make up about 75% to 80% of all the antibodies in the body. Unlike IgM antibodies, the body produces IgG antibodies much later.

As a result, IgG antibodies can only be detected in the later course of an illness. According to the FDA’s Fact Sheet for Healthcare Providers, IgG antibodies do not begin to appear until 7-10 days after infection. Therefore, the IgG panels are used to detect “recent infection” or “in-recovery” states.

Applications for Antibody Testing

As described above, a positive test result with the qSARS-CoV-2 IgG/IgM Rapid Test means that the patient has IgG and/or IgM antibodies present and may have been exposed to COVID-19. However, antibody testing tells us more about the patient.

Although IgM antibodies are produced first in response to an infection, they are also short-lived and have a half-life of 5-6 days. Therefore, if a patient has a positive IgM and a negative IgG, this indicates that the infection is active. On the other hand, if a patient has a positive IgG and a negative IgM, this portrays that the virus has run its course and this can be a signal of protection against COVID-19. In essence, serological testing is useful for determining which individuals can resume their normal activities due to their body’s new resistance to SARS-CoV-2.

One major application for antibody testing is the ability to detect which healthcare workers can return to work after they have been infected. These workers are needed on the front lines to care for patients who are infected by COVID-19. For them to be successful at their job, they need to stay healthy. Serological testing is important for this category of workers to ensure that they are protected against the virus.

Applications for antibody testing go beyond just healthcare workers. The same testing method can be applied to decide whether all essential workers can go back to work. Essential workers that may benefit from antibody testing include law enforcement officials, grocery store cashiers, bus drivers, firefighters, delivery workers, people in the food business, security guards, and maintenance workers.

Immunoglobulin Replacement Therapy (Antibody Therapy)

Immunoglobulin (Ig) replacement therapy is the process of transfusing a donor’s antibodies, also known as intravenous immunoglobulin (IVIG), into a recipient’s blood to help them fight microorganisms that cause infections.

Most applications of Ig therapy have been for patients with immune deficiencies. In the case of COVID-19, researchers are investigating whether plasma transfusions of IVIG can potentially help save lives and alleviate the COVID-19 epidemic.

During Ig therapy, prepared immunoglobulin is injected into the veins of the patient. Next, the medicine flows from a bag through a tube into the arm. The dosage typically depends on the weight of the patient.

How Successful has Immunoglobulin Replacement Therapy been?

For the past four decades, Ig therapy has been the standard of care in patients who cannot naturally produce antibodies. Over 75% of the IVIg transfused in the US has been to patients with autoimmune or inflammatory conditions.

Ig therapy has been largely successful. However, several studies have also documented adverse effects during this treatment, including renal impairment, hematologic disorders, and electrolyte imbalance.

What Hospitals are Using Immunoglobulin Therapy to Treat COVID-19?

For years, immunoglobulin (IgG) replacement therapy (transferring IgG antibodies from a donor to a patient) has been a lifesaver for people whose bodies can’t make enough antibodies, for example, individuals with primary immunodeficiency disease (PIDD). Without this therapy, people with PIDD often succumb to severe infections.

Researchers have now considered immunoglobulin therapy for treating patients infected with SARS-CoV-2. The results from antibody testing are important because they identify recovered COVID-19 patients who currently have positive IgG test results, who can then become potential IgG donors.

The first physicians and scientists to test plasma transfusions against COVID-19 are from Houston Methodist, Texas, where a newly recovered COVID-19 patient donated blood to two ill patients. The recovered patient was in good health for more than two weeks before choosing to donate plasma.

The FDA classified Houston Methodist’s method as an emergency investigational new drug protocol (eIND), which means that the FDA has to approve the process for every patient.

According to James Musser M.D., Ph.D., pathology and genomic medicine chair at Houston Methodist Research Institute, “We, the nation and the world are not going to have a vaccine for quite some time...so this is potentially—if it were safe and efficacious—something that could be done relatively soon.”

“Coronavirus Testing Explained” Infographic Learn about Test Types, Coronavirus antibodies, and the COVID-19 “Coronavirus” IGG/IGM Rapid Test Kit.

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